Hitherto, glass antennas for receiving AM radio broadcast waves and FM radio broadcast waves achieve higher gains as areas surrounded by antenna strips become larger. Accordingly, these glass antennas are often provided on the rear window glass of the automobile which is easy to ensure a large area for obtaining a good reception gain. Furthermore, the rear window glass of the automobile is often formed on its central region with defogging heater strips (defogger) for ensuring rear visibility at the driving in the rain. Therefore, in case that the glass antenna is formed on the rear window glass, it has been forced to be formed in a blank space above or below the defogging heater strips.
For example, Japanese Patent Application Publication No. 2008-35412 discloses a glass antenna for a sedan-type automobile which is provided in blank spaces above and below defogging heater strips of a rear window glass of the automobile. This antenna includes a grounded antenna for AM/FM radios which is provided in the blank space above the defogging heating strips, and a grounded sub antenna for FM radio which is provided in the blank space below the defogging heating strips. Horizontal strips of the sub antenna are disposed to be apart from horizontal heating strips of the defogging heater strips, and/or horizontal strips bifurcating and extending from the horizontal heater strips of the defogging heater strips so as not to generate dip in the frequency characteristic. The interference by a metal frame of a movable backseat is prevented, and thereby the generation of the dip is prevented (Patent Document 1).
Moreover, Japanese Patent Application Publication No. 11-284421 discloses a glass antenna for a vehicle which uses, as an antenna, a defogger constituted by a plurality of heating conductive strips disposed on a rear window glass of the vehicle, and bus bars disposed on outsides of the heating conductive strips. In this glass antenna, a loop element is disposed in a blank space above or below the defogger. This element is directly connected with a part of the defogger. The electric power is fed from this element (Patent Document 2).
Moreover, Japanese Patent Application Publication No. 8-321711 discloses a high frequency glass antenna. The high frequency glass antenna includes an antenna conductor provided on a glass sheet of a window of an automobile, and another antenna conductor (6) which is provided on the glass sheet of the window of the automobile, and which is disposed adjacent to the antenna conductor with a predetermined distance so as to achieve the capacitive coupling. Moreover, the high frequency glass antenna includes another antenna conductor (16) which is provided on the glass sheet of the window, and is different from the antenna conductor and the antenna conductor (6). The antenna conductor (6) has a loop shaped portion in the electrical sense. The antenna conductor (6) is disposed adjacent to the antenna conductor (16) with a predetermined distance so as to achieve the capacitive coupling. Furthermore, the antenna conductor (16) is disposed adjacent to an opening portion (100) of an automobile body with a predetermined distance to achieve the capacitive coupling (Patent Document 3).